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There is now an alternative to solid tantalum capacitors

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Roger Tall (Roger Tall) wrote that the latest developments in polymer cathode technology and improvements to strengthen the tantalum supply chain have enabled more designers to choose polymer tantalum capacitors as an alternative to traditional solid tantalum capacitors.

When specifying an ideal capacitor, most designers will start with high volumetric efficiency and then consider the small package and capacitance stability within the range of applied voltage, frequency, temperature, and time.

Low equivalent series resistance (ESR), noise-free operation, high ripple current handling capability and decades of life expectancy will also appear in the technology wish list.

Conventional solid, MnO

Tantalum capacitors meet many of these standards, and the latest polymer tantalum has significantly improved performance.

At higher frequencies up to 500kHz, the capacitor retention capability is improved and the ESR is reduced to 5mΩ. The rated voltage of polymer tantalum is as high as 75V, and has a more relaxed derating criterion.

The inherent risk of fire or smoke during short-circuit failure of solid tantalum capacitors has also been eliminated through the benign failure mode of polymer tantalum.

figure 1

As time, temperature and voltage change, the capacitance stability of polymer tantalum capacitors exceeds that of MLCC. Although MLCC is prone to aging, polymer tantalum can achieve long-term stability over a 20-year service life. This long life also makes polymer tantalum a viable alternative to aluminum electrolytic capacitors, which can dry out during use and may need to be reshaped after a shelf life of 2 years or less.

When polymer tantalum capacitors work at temperatures as low as -55°C, there is no significant change in capacitance, which is the main advantage over capacitors containing liquid electrolytes. However, their upper limit temperature is 125°C, which is lower than MnO.

Including a version of the capacitor that can work at temperatures up to 200°C.

The relatively high equivalent series resistance (ESR) has always been the weakness of conventional MnO

Usually a capacitor with an ESR of 40 to 50 mΩ. Capacitance attenuation experienced by MnO

Therefore, frequencies higher than 10kHz limit their use in certain applications. In contrast, polymer technology can reduce ESR to 5mΩ, ensuring that useful capacitance is available at frequencies up to 500kHz.

Tantalum is not the only capacitor technology that uses polymers to enhance stability. For frequencies close to 1MHz, the 2mΩESR achieved by polymer aluminum capacitors can provide a higher capacitance retention rate without increasing design complexity. However, this reduced ESR must be weighed against the lower maximum capacitance of polymer aluminum, which is only 50% to 80% of polymer tantalum in the same package.

For applications where miniaturization is a priority, this may be critical. The smallest case size provided by polymer aluminum capacitors is 7343, while the smallest case size of polymer tantalum is 0805. The voltage range of polymer aluminum capacitors is also limited to 35V, while polymer tantalum can be used in applications up to 75V.

The choice of tantalum capacitors is not limited to electrical performance, but may also be affected by ethical and commercial issues. Many tantalum ores in the world are mined in the Democratic Republic of the Congo (DRC), where militiamen have used tantalum and other mines to fund their activities during years of armed conflict, and severely violated human rights.

The world's response to this is the introduction of US laws, such as the 2009 Congo Conflict Minerals Act and the new EU law announced in March 2017, which will take effect in 2021. Both regulations require companies to provide the necessary traceability to ensure that their supply chains are free of conflict minerals.

Many companies believe that the simplest compliance strategy is to avoid any trade with DRC.

Capacitor manufacturer Kemet has fundamentally answered the ethical questions surrounding the procurement of tantalum ore by taking a more radical approach to eliminate conflict minerals from the supply chain. By cooperating with a certified conflict-free mine in the Democratic Republic of Congo, Kemet can ensure that the mine operates in accordance with iTSCi and other regulations and distributes income fairly to miners and local communities.

This not only frees OEMs from the ethical constraints of using tantalum capacitors, but also helps eliminate supply risks, price instability and fluctuations in delivery time.

The combination of low ESR with higher voltage, stability and frequency, as well as more stable and ethical tantalum procurement, means that designers can now apply the advantages of polymer tantalum technology to a wider range of applications.

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